The present disclosure relates to spread-spectrum communications and, in particular, to a method and apparatus for providing a multi-stage automatic gain control for spread-spectrum receivers.
In typical communications systems, a gain is used to adjust the power level of a received signal. The gain function of a communications receiver generates an error that is used to compute an amplifier gain. The gain operation is intended to bring the received signal to a known and constant power level.
Unfortunately, the channel conditions in a mobile environment change very rapidly, and the Signal-to-Noise Ratio (“SNR”) levels in a spread-spectrum system, such as, for example, a Wideband Code Division Multiple Access (“WCDMA”) system, are low. Typical systems implement a single gain loop according to a compromise based on anticipated operating conditions. Thus, a fast gain loop may be able to track sudden changes, but has the drawback that it is generally noisy. In contrast, a slow gain loop may be able to average out the noise, but has the drawback that it is generally not able to keep up with sudden channel changes. What is needed is a gain solution capable of tracking sudden changes while averaging out noise in a spread-spectrum system.